Two men have been arrested on terror-related charges in California and Texas, according to authorities.

The arrests were made after the accused allegedly sought to aid terrorist organizations affiliated with Islamic State (IS), say court documents. One of the two arrested is a refugee from Syria, raising fresh concerns over the US program to resettle refugees from Syria and other countries with territory controlled by terrorists.

"This is precisely why I called for a halt to refugees entering the US from countries substantially controlled by terrorists," said Texas Gov. Greg Abbott. "I once again urge the President to halt the resettlement of these refugees in the United States until there is an effective vetting process that will ensure refugees do not compromise the safety of Americans and Texans."

Concerns over the US refugee program arose following the November terrorist attacks in Paris. Initial reports suggested that one of the attackers may have been an asylum-seeking refugee from Syria, prompting governors from more than half of US states to publicly oppose having Syrian refugees settle in their states.

Refugee resettlement programs are under managed by the federal government, and the Obama administration has maintained that states and their governors do not have control over where refugees settle.

On Thursday, the state of Alabama sued the federal government over the resettlement program, saying that the government is not providing the state with sufficient information about the backgrounds of incoming refugees. Texas has also filed suit against the government over the resettlement of Syrian refugees.

The federal government and migration experts have said that lengthy process of applying for asylum as a refugee makes that avenue one of the least likely paths for terrorists to take into the United States. However, the apparent connection between one of the suspects arrested this week and the Islamic State suggests that it it in fact possible for militant fighters to gain access to the US through refugee programs.

In Houston, Omar Faraj Saeed al-Hardan, 24, was indicted on charges of seeking to provide material support to terrorist organizations affiliated with Islamic State.

A second arrest took place in Sacramento, Calif. Criminal complaints that became public Thursday indicate Aws Mohammed Younis al-Jayab, 23, traveled to Syria to fight in the civil war and lied to investigators.

Mr. Jayab, of Sacramento, had criticized Islamic State on social media and earlier said he would never join the group because of their killings of Muslims. His social media and other accounts suggested that upon his arrival to the United States, he had a desire to return in Syria to fight, according to authorities. Some of his posts say he wants to return to Syria to “work,” a term the FBI believes referenced “assisting in and supporting violent jihad.”

Jayab immigrated to the United States in 2012, after having been involved in the fighting in Syria since he was 16, information that was kept from citizenship officials. He left the Untied States in 2013, but returned and settled in Sacramento in 2014.

The affidavit details online conversations from 2013 during which Jayab described fighting in Syria, executing three Syrian government soldiers, and emptying seven clips from his assault rifle during a battle.

“While he represented a potential safety threat, there is no indication that he planned any acts of terrorism in this country," US Attorney Benjamin Wagner said to Reuters.

How Jayab and Mr. Hardan are connected is still unknown. The affidavit for Jayab revealed communications with an unknown person in Texas, seeking to get training with various weapons in 2013. It is unclear if Hardan was involved.

Jayab is scheduled to appear in federal court in Sacramento on Friday.